Mercury switch



Sept. 27, 1966 c H FOSTER 3,274,939

MERCURY SWITCH Filed July 29, 1964 INVENTOR CHARLES: H. FO TER BYWJM,

ATTORNEYS United States Patent 3,274,939 MERCURY SWITCH Charles H. Foster, 211 W. 6th St., Rutherfordton, N.C. Filed July 29, 1964, Ser. No. 386,089 1 Claim. (Cl. 103-25) This invention relates to control devices and more particularly to control devices for a pump wherein the pump is operated only within a predetermined range of fluid pressure.

The desirability of operating pumps only within a predetermined range of fluid pressures on the output side thereof is Well known. For example, if the output fluid pressure of a pump exceeds a predetermined maximum, the pump and/or drive means therefor may be overloaded and damaged and the pipes and other equipment connected to the pump may rupture or break. Additionally, if this fluid pressure falls below a predetermined minimum due to a leak in the system or for other reasons, the pump will be subject to continuous operation for an a suitable motor 11, to which electrical current is supplied by an electrical circuit, generally indicated by the reference numeral 12 (FIGURE 1).

The circuit 12 includes a male plug 13 adapted for insertion into any suitable electrical outlet. A line 14 is connected at one end to plug 13 and at its other end to one side of motor 11. A line '15 is connected at one end to the other side of motor 11 and is connected at its other end to one side of a normally open, manually operable switch 16, the other side of which is connected to plug 13 by a line 17 to complete a first or primary circuit to motor 11.

A pressure gage, generally indicated by the reference numeral 20, is operably connected to the output side of pump 10 by a fluid pressure line 21 for sensing the output fluid pressure thereof. The pressure gage includes a housing 22, a transparent cover plate 23 mounted extended time period which would result in excessive I wear thereon and possible overheating of the pump and/ or drive means therefor, and/ or undesirable fluid loss will occur.

Various conventional control devices for pumps, purportedly for operating the same within a predetermined range of fluid pressures, have been proposed, but such conventional control devices are usually mechanically operated switches which do not have the required sensitivity and which frequently fail to operate successfully due to friction, wear, or malfunction of the mechanical linkage thereof. Such conventional switches are usually associated with pressure gage and frequently adversely affect the operation of the pressure gage. Also, such conventional control devices are relatively complicated and expensive since they normally require two switches to properly control the pump within the predetermined range of pressure.

It is therefore an object of this invention to provide a novel control device for use with a pressure gage of a pump to control the operation of the pump to stop the same when the fluid pressure rises above a predetermined maximum or drops below a predetermined minimum and wherein the deficiencies of prior control devices are obviated.

A more specific object of the present invention is to provide a novel, single mercury switch operatively asso= ciated with a pressure gage and connected to a pump for controlling the operation of the pump whereby the same is operated only within a predetermined range of fluid pressure and wherein this range of pressure may be varied.

It is a further object of this invention to provide a novel construction for a rotatable mercury switch which may be used in conjunction with a pressure gage of a pump system or with similar mechanisms, and wherein increased sensitivity is provided.

Some of the objects of the invention having been stated, other objects will appear as the description proceeds when taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a partially schematic view of a pump system having a pressure gage andutilizing the control device of this invention;

FIGURE 2 is a view taken substantially along the line 2-2 of FIGURE 1;

FIGURE 3 is a cross-sectional view taken substantially along the line 33 of FIGURE 2; and

FIGURE 4 is a perspective view of the mercury switch of this invention.

Referring to the drawings, there is shown schematically in FIGURE 1 a pump 10 which may be of any conventional type and construction. The pump 10 is driven by on the housing 22, a transparent pressure indicating face 24 carried within the housing 22 and graduated around the circumference thereof into numerical increments of fluid pressure, and a pointer 25 for indicating the output fluid pressure of pump 10. Pointer 25 is carried on a hollow shaft 26 which is mounted in a bearing 27 carried by face 24 of the gage 20. The pointer 25 is actuated in conventional manner (not shown) through shaft 26. i For stopping operation of motor 11 and hence pump 10 when the output pressure sensed by gage 20 drops below a predetermined minimum or rise above a predetermined maximum, a mercury switch, generally indicated by the reference numeral 30, is provided within housing 21 of pressure gage 20 behind transparent face 24. The mercury switch 30 comprises a generally cylindrical elongate body portion 31 containing a small amount of mercury M .and having a pair of angular, downwardly extending and converging bottom walls 32 and 33 meeting at a vertex 34 to define an offset portion 35 in the body portion 31. The angular disposition of the walls 32 and 33 is important to ensure the proper location of the mercury within the switch 30 for opening and closing the switch at desired rotary positions of the switch 30 and thereby to provide the desired sensitivity of switch 30 to minute changes in pressure at the predetermined minimum and maximum pressures, as will become more apparent hereinafter.

The bottom wall 32, as may be seen in FIGURE 3, forms an angle of approximately 12 with a line through the vertex 34 of ofl'set portion 35 and parallel to the longitudinal axis of switch 30 and bottom wall 33 forms an angle of approximately 30 with a line through vertex 34 and perpendicular to the longitudinal axis of switch 30. Therefore, an included angle of approximately 108 is providedbetween walls 32 and 33 which means that switch 30 is actuated or closed through an arc of. rota.- tive movement of about 70 Therefore, if the longitudinal axis of switch 30 is disposed parallel to pointer 25, the range of pressure within which pump 10 is operative is about 25 to 60 p.s.i. with the particular calibration of gage 20 illustrated in the drawing. Of course, this range would vary with gages of different calibration. Also, the extent of this operative range of pressure for pump 10, i.e., the pressure difference between the predetermined minimum and maximum, may be varied by varying the angular relationship of walls 32 and 33' to vary the included angle at the vertex 34. In this respect, this included angle is inversely proportional to this range of pressure and hence the smaller the included angle, the larger the operative range of pressure and vice versa.

The mercury switch 30 has one end thereof closed by a cap 36 which is removable for insertion of the mercury M therein. The switch 30 further includes a pair of spaced electrical contacts 40 and 41 mounted within offset portion 35 at the vertex 34 thereof. Contact 40 is connected by a line 42 to the side of switch 16 to which line 17 is connected and contact 41 is connected by a line 43 to the side of motor 11 to which line is connected. Switch 30 is thereby connected in parallel to manually operable switch 16.

Mercury switch 30 also includes a mounting portion 44 formed integral with offset portion 35 and has an opening 45 therein immediately beneath vertex 34 of offset portion 35. A shaft 46 tightly extends through opening 45 to mount switch 30 thereon for rotation therewith and also extends through hollow shaft 26. Shaft 46 is journaled at one end in a sleeve bearing 47 mounted on the rear wall of housing 21 of gage and has a knob 50 mounted on the other end thereof for manual rotation of shaft 46 and hence switch 30 to vary the angular position of switch 30 to pointer and to thereby vary the amount of pressures which shall constitute the predetermined minimum and maximum. Another knob 51 is mounted on hollow shaft 26 and has a set screw 52 therein for connecting shafts 26 and 46 for concurrent rotation to secure the same in any desired relative adjusted position.

To operate the pump system above described, the male plug 13 is inserted into any electrical outlet to cause electricity to flow into the circuit 12. Inasmuch as the pump 10 is not now being operated by the motor 11, the output fluid pressure thereof is at 0 p.s.i. and the mercury M in mercury switch is located in the forward end of the switch and will not complete the flow of electricity between contacts 40 .and 41. Thus, to start the motor 11 to operate the pump 10 to build up the fluid pressure to the predetermined minimum of about 25 p.s.i., it is necessaly to manually close switch 16 to complete the primary circuit to motor 11 and to hold this switch closed until the output pressure of pump 10 reaches the predetermined minimum.

When this minimum pressure is reached, the mercury switch 30 will have been rotated to a position wherein bottom Wall 32 is just above the horizontal, which will allow the mercury M to flow into the offset portion and bridge contacts and 41 to close the switch 30. Then, switch 16 may be disengaged and electricity will flow through the mercury switch 30 to the motor 11 to operate the pump 10. This operation Will continue as long as the fluid pressure in pump 10 is between about 25 p.s.i. and 60 p.s.i. in the arrangement illustrated in the drawing. However, if the output pressure of pump 10 should rise above about 60 p.s.i., the mercury switch 30 will be rotated to a position wherein wall 33 is just below horizontal such that the mercury will flow out of the offset portion 35 and open switch 30. When the pressure has been reduced below about 60 p.s.i., mercury switch 30 will be rotated to a position where the mercury will again flow into the offset portion 35 and close switch 30. If the output fluid pressure of pump 10 falls below about 25 p.s.i., the mercury switch 30 will be rotated to such as position that the mercury will again flow out of the offset portion 35 into the forward end of the switch to open the switch .and break the flow of electricity between contacts 40 and 41 and thus stop operation of motor 11. If this above condition occurs, the malfunction may be corrected and the switch 16 may be again engaged to build the output pressure of the pump 10 up to about 25 p.s.i. to allow the mercury switch 30 to control the supply of electricity to the motor 11.

Thus, it may be seen that an improved construction for a mercury switch has been provided which may be utilized in a pump system to provide the desired sensitivity to stop operation of the pump when the fluid pressure therein has dropped below a predetermined minimum or when the fluid pressure therein has risen above a predetermined maximum.

In the drawings and specification there has been set forth a preferred embodiment of this invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purposes of limitation, the scope of the invention being clefined in the claim.

What is claimed is:

The combination of a pump, motor means for operating said pump, a pressure gage connected to said pump for indicating the output fluid pressure thereof and including rotatable pressure responsive shaft means mounted within said gage and having a pressure indicating pointer mounted thereon, a mercury switch rotatably mounted on said gage shaft means for rotation therewith and operatively connected to said motor means for stopping operation of said pump at predetermined maximum and minimum output pump pressures and for permitting operation of said pump Within an operating range of pressures between the predetermined maximum and minimum pressures, said mercury switch being adjustably mounted on said pressure indicating gage shaft means for varying said predetermined maximum and minimum pressures at which said mercury switch will stop operation of said pump, said mercury switch comprising a generally cylindrical elongate body portion containing mercury and having an offset portion therein intermediate the ends thereof defined by a pair of angular downwardly extending and converging bottom walls meeting at a vertex, the included angle between said bottom walls of said offset portion being approximately 108 and thereby providing a range of operating pump pressures corresponding to an arc of movement of about of the pointer of said pressure gage, and a pair of spaced electrical contacts mounted within said offset portion at the vertex thereof, the mercury within said switch being located in said offset portion at the vertex thereof when the output pressure of said pump is within the range of operating pressures to close said switch for operating said pump and being located away from the vertex of said offset portion when the output pressure of said pump is above the predetermined maximum pressure and below the predetermined minimum pressure to open said switch for stopping operation of said pump, and a manually operated switch operatively connected to said motor means in parallel to said mercury switch for operating said pump at any pressure.

References Cited by the Examiner UNITED STATES PATENTS 1,952,265 3/1934 Leland 103-25 2,164,113 6/1939 Kolb 200152 2,734,107 2/1956 Reichel 200-452 2,741,987 4/1956 Murphy et al. 103-25 3,013,624 12/1961 DeRemer et 'al. 20061.52 3,121,286 2/1964 Schneiderman 20061.47

MARK NEWMAN, Primary Examiner.

SAMUEL LEVINE, Examiner.

W. L. FREEH, Assistant Examiner. 

